1. Field of the Invention
This invention relates to a catalyst system suitable for the polymerization of vinyl compounds. More specifically, it relates to a chelate of a hydrocarbyl lithium compound and a bicyclic compound having two heterocyclic ring structures joined together through nitrogen atoms in the respective rings by means of a bridge of 1-4 carbon atoms, each heterocyclic ring having at least a second heteroatom in the ring structure thereof selected from NR, O, S and PR. Moreover, this invention relates to a process of polymerizing vinyl compounds using such a catalyst. Still more specifically this process relates to a process of polymerizing conjugated dienes to prepare highly crystalline polymers, for example, polymerizing butadiene to polymers containing a high percentage of syndiotactic polybutadiene.
2. Related Prior Art
U.S. Pat. No. 3,451,988 describes a polymerization catalyst and a process for polymerizing vinyl compounds therewith that utilizes hydrocarbyl lithium and magnesium compounds together with a bifunctional Lewis base which is described as including tertiary diamines in which the nitrogen atoms in the diamines are bridged by 1-4 carbon atoms. Although the tetramethylethylene diamine (TMEDA) appears to be the preferred diamine since it is used more often in the examples, 1,2-dipiperidino ethane, as well as others, are also indicated as suitable.
However, the highest 1,2 contents of polybutadiene reported for TMEDA are the 87.5% and 89% reported in Col. 16. The highest 1,2 content reported in the patent is the 95% reported for tetrahydrofuran (THF), also in Col. 16, but this is associated with a conversion or yield of only 33%. Moreover, with the preferred TMEDA there is subsequent methylation as described in Col. 15 of the patent.